I got my kooks 1 7/8 mid lengths because i still wanted to use my lethal catless H-pipe. I didnt want an X, and didnt like any of the LT H-pipe options. For me it was pretty straight forward.
You may give up a little hp to a long tube set up, but may gain a little more tq in the process. I do believe the Kooks make damn good power, i also believe a good long tube set up may make more, but the kooks are cheaper and i dont think the LT are "enough better" to justify the price. I believe a good set of Shorties will outperform a cheap set of long tubes. Just my opinion and thought process though.